Hearing is believing: Sounds can alter our visual perception

Perception generally feels effortless. If you hear a bird chirping and look out the window, it hardly feels like your brain has done anything at all when you recognize that chirping critter on your windowsill as a bird.

In fact, research in Psychological Science suggests that these kinds of audio cues can not only help us to recognize objects more quickly but can even alter our visual perception. That is, pair birdsong with a bird and we see a bird — but replace that birdsong with a squirrel’s chatter, and we’re not quite so sure what we’re looking at.

“Your brain spends a significant amount of energy to process the sensory information in the world and to give you that feeling of a full and seamless perception,” said lead author Jamal R. Williams (University of California, San Diego) in an interview. “One way that it does this is by making inferences about what sorts of information should be expected.”

Although these “informed guesses” can help us to process information more quickly, they can also lead us astray when what we’re hearing doesn’t match up with what we expect to see, said Williams, who conducted this research with Yuri A. Markov, Natalia A. Tiurina (École Polytechnique Fédérale de Lausanne), and Viola S. Störmer (University of California, San Diego and Dartmouth College).

“Even when people are confident in their perception, sounds reliably altered them away from the true visual features that were shown,” Williams said.

In their first experiment, Williams and colleagues presented 40 participants with figures that depicted two objects at various stages of morphing into one another, such as a bird turning into a plane. During this visual discrimination phase, the researchers also played one of two types of sounds: a related sound (in the bird/plane example, a birdsong or the buzz of a plane) or an unrelated sound like that of a hammer hitting a nail.

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